La percezione del movimento

La selettività neurale per il movimento

Il detettore (parziale) di Reichardt

PreferitaNulla

Il detettore (completo) di Reichardt

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Movie

L’illusione dell’insegna dei barbieri

demo

V1

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Waterfall illusion (Addams, 1834)

Positional motion aftereffect (PMAE)

Snowden (1998) Curr. Biol.Nishida & Johnson (1999) Nature

Movimento complesso: flusso ottica

Lettura

• Morrone, M.C., Burr, D.C., and Vaina, L. (1995). Two stages of visual processing for radial and circular motion. Nature 376, 507-509.

• Morrone, M.C., Tosetti, M., Montanaro, D., Burr, D.C., Fiorentini, A., and Cioni, G. (2000). A cortical area that responds specifically to optic flow, revealed by function Magnetic Resonance Imaging. Nature Neuroscience 3, 1322-1328.

Neural response in MSTdDuffy & Wurtz, 1991

Psychophysical evidence for detection of optic flow in

humans?

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Spatial summation

Signal-to-noise Predictions

• S α Nsectors

• σ2 α Nsectors σ α √Nsectors

• S/σ α √Nsectors

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Signal-to-noise Predictions

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• σ2 = k (constant)

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Spatial summation of contrast

Two-stage motion analysis

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Local motion detectorsContrast thresholded

Complex motionintegrator

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Summation constants

Segmentation has different temporal integration.

Even a weak signal embedded in noise can be seen given a long enough view

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DCB Radial Circular Trans

Spatial summation for flow is extensive

Spatial summation of contrast sensitivity of sinusoids

Anderson and Burr, 1987

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Spatial Frequency (c/deg)

Interim Conclusions•There exists psychophysical evidence for detectors tuned to complex optical flow.

•Evidence suggest that the detectors are “second-stage” after contrast thresholding.

•Temporal summation is extensive: ~ 3 sec.

•Spatial summation is extensive, ~ 70°.

A neural centre for optic flow?

FLOW (30 s) NOISE (30 s)2 s 2 s 2 s 2 sInverting Direction

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Experiment in dos

Biological motion

http://www.biomotionlab.ca/Demos/BMLwalker.html

Adult plasticity: paraplegia affects perception of “biological motion”

The mirror system?(Giacomo Rizzolatti)

Sensitivity impaired for biological motion but not contrast sensitivity for orientation

Controls

Patients

Arrighi et al., Current Biol. (2011)

Paraplegic sensitivity worse for visual motion, especially biological

motion

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Motion CS Static CSBM:DirectionDiscrimin

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TranslatingWalker

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Arrighi et al., Current Biol. (2011)

The results point to shared neural circuits for production and perception of movement

– the mirror system?

CONCLUSIONS Paraplegic adults have reduced sensitivity to

biological motion: shared neural mechanisms for perception and production of motion

L’illusione di Ouchi

L’illusione di Ouchi